Biomechanical investigations of different osteosynthesis procedures in the proximal tibia-introduction of a new measuring system]

In this article a new measuring system for biomechanical studies of various osteosynthesis procedures on the tibia is described. The paired tibias are osteotomized and embedded in PMMA in accordance with a randomization protocol. Testing is then carried out under nonaxial loading at 350 N, 600 N and 900 N, uniaxial bending applying a force of 12 Nm, and torsion at a force of 5 Nm in a universal pneumatic testing machine. Ultrasonic sensors pick up movement at the fracture gap under external loading. Testing of the measuring setup has been successful, and relevant results were obtained.     

Novel way of measuring the fracture toughness of leaves and other thin films using a single inclined razor blade

A new test for measuring leaf fracture toughness by cutting with a single inclined razor blade is described here, this having been developed to overcome some of the inadequacies of conventional double-bladed cutting tests, such as scissoring and shearing. The accuracy and precision of this test were determined by measuring the fracture toughness of various leaf types and homogeneous films, and comparing the results with those obtained by scissoring. The new test was found to display a low friction of cutting with great precision in measurements. Fracture toughness measurements of the specimens were considerably lower for the new test than those obtained by scissoring, owing to greater blade sharpness and reduced damage to the specimens during cutting. Despite this, the rankings of fracture toughness measurements for the specimens are similar for both the new test and scissoring, thus demonstrating the test's consistency with scissoring. The new test was found to be successful in measuring the fracture toughness of leaf blades and other thin, film-like materials. It was also able to overcome some of the difficulties of conventional double-bladed cutting tests, especially the estimation of energy expenditure that is extraneous to the work of cutting.     

Rapid alignment of the interference mask in the ultracentrifuge

A procedure is given for measuring the degree of misalignment of the interference mask in the analytical ultracentrifuge. A simple apparatus is described which allows the mask alignment to be corrected by precise lateral movement of the mask.     

A method to measure the duration of DNA synthesis and the potential doubling time from a single sample

A method is described whereby the DNA synthesis time, Ts, can be calculated using data of a single sample of cells taken several hours after labelling with bromodeoxyuridine (BrdUrd). The method involves a simple calculation using flow cytometry data of BrdUrd incorporation (green fluorescence, FITC-labelled anti-BrdUrd-DNA antibody) and total DNA content (red fluorescence, propidium iodide). The movement of BrdUrd-labelled cells through the S phase can be quantified by measuring their mean red fluorescence relative to that of G1 and G2 cells. Assuming the movement of the labelled cells toward G2 is linear with time, Ts can be calculated by measuring their relative movement at any one time. The method was tested on cells in vitro and on bone marrow and tumor cells in vivo. Reasonable agreement was seen with published estimates of Ts for these tissues.     

Trapdoor fracture of the orbit in a pediatric population

Orbital-floor blowout fractures of the trapdoor variety, first described by Soll and Poley, have also appeared in the French and Japanese literature. The trapdoor fracture is described as a pure orbital-floor fracture, linear in form and hinged medially, which allows herniation of orbital contents through the fracture and then entraps these herniated contents. A review of the orbital-floor fracture literature reveals a high incidence of persistent diplopia associated with ocular-muscle entrapment, which may later necessitate corrective surgery of extraocular muscles. Recent publications in the ophthalmologic literature have stressed the importance of early surgical intervention. This article reports a retrospective series of 19 pediatric patients (age range, 5 to 16 years) who presented to two institutions. All patients had radiographic confirmation of a trapdoor fracture. Physical examination demonstrated a high association between these fractures and restricted ocular motility (17 of the 19 patients). In the cases with trapdoor fracture and restricted ocular movement, early intervention was associated with better postoperative function. It is thus recommended that the symptomatic trapdoor orbit fracture be considered an urgent indication for surgical intervention. Practitioners therefore must have a high index of suspicion for these injuries. Prompt diagnosis is critical to maximize clinical outcome.     

A nephelometer for measurement of nematode populations

A nephelometer for measuring nematode populations is described in which a standard 18 mm culture tube is illuminated from below, and four selenium photocells are placed radially at 90° about the tube. This design minimizes fluctuations in readings due to movement of the nematodes at low population densities.     

Measurement of fracture movement in patients treated with unilateral external skeletal fixation

Axial movement occurring at the fracture site has been determined in a group of healing tibial fractures treated by external skeletal fixation. Fracture movement was determined via a strain gauge transducer which was attached to the column of the external fixator and measured the deflection of the bone screw adjacent to the fracture site and the active loading or weight bearing given by the patient to the fractured limb was monitored using a force platform. The results for 27 subjects show that, with a rigid unilateral fixator, the axial movement occurring at the fracture site was initially small (mean = 0.28 mm at 5 weeks post fracture). This movement increases to reach a mean maximum value of 0.43 mm at 11 weeks post-fracture and then decreases, despite increased weight bearing, as fracture healing progresses. In the early stages of healing, the movement can be increased slightly if the fixator is fitted with a module which permits additional fracture site movement, although the resultant increase in movement is only a small proportion of the potential available with this module.     

In situ comparison of A-mode ultrasound tracking system and skin-mounted markers for measuring kinematics of the lower extremity

Skin-mounted marker based motion capture systems are widely used in measuring the movement of human joints. Kinematic measurements associated with skin-mounted markers are subject to soft tissue artifacts (STA), since the markers follow skin movement, thus generating errors when used to represent motions of underlying bone segments. We present a novel ultrasound tracking system that is capable of directly measuring tibial and femoral bone surfaces during dynamic motions, and subsequently measuring six-degree-of-freedom (6-DOF) tibiofemoral kinematics. The aim of this study is to quantitatively compare the accuracy of tibiofemoral kinematics estimated by the ultrasound tracking system and by a conventional skin-mounted marker based motion capture system in a cadaveric experimental scenario. Two typical tibiofemoral joint models (spherical and hinge models) were used to derive relevant kinematic outcomes. Intra-cortical bone pins equipped with optical markers were inserted in the tibial and femoral bones to serve as a reference to provide ground truth kinematics. The ultrasound tracking system resulted in lower kinematic errors than the skin-mounted markers (the ultrasound tracking system: maximum root-mean-square (RMS) error 3.44° for rotations and 4.88 mm for translations, skin-mounted markers with the spherical joint model: 6.32° and 6.26 mm, the hinge model: 6.38° and 6.52 mm). Our proposed ultrasound tracking system has the potential of measuring direct bone kinematics, thereby mitigating the influence and propagation of STA. Consequently, this technique could be considered as an alternative method for measuring 6-DOF tibiofemoral kinematics, which may be adopted in gait analysis and clinical practice.     

Concept for development of new individual treatment devices in orthodontics using 3-dimensional numerical simulation of bone remodeling]

The present study is part of a research project that includes different components for the simulation of orthodontic tooth movement and comparing experimental results. This concept includes the development of a bone remodelling algorithm, as well as experimental studies on tooth movement. After the acquisition and evaluation of specific experimental data of the patient's situation, the individual components have to be integrated to verify and forecast tooth movement. The aim is to design individual treatment devices as well as to shorten treatment while making it more effective. The geometry of the teeth and that of the surrounding alveolar bone both influence the orthodontic tooth movement. For this reason, an exact morphological tooth model for the valid simulation of the tooth movement is needed, and can be constructed from computed tomography data. Simulation of tooth movement can then be compared with "in vivo" measurements of the orthodontic tooth movement. In this study, a specially developed hybrid retraction spring is employed. This spring enables the application of a defined, almost constant force system. The "in vivo" determined tooth movement is simulated with the aid of special positioning and measuring devices. Meanwhile, the active force system can be determined by 6-component force/moment sensors. The experimentally measured force system, "in vivo" measurements of tooth movement and the CT model are now available for numerical simulation for the first time.     

Figure-ground discrimination by relative movement in the visual system of the fly

The visual system of the fly performs various computations on photoreceptor outputs. The detection and measurement of movement is based on simple nonlinear multiplication-like interactions between adjacent pairs and groups of photoreceptors. The position of a small contrasted object against a uniform background is measured, at least in part, by (formally) 1-input nonlinear flicker detectors. A fly can also detect and discriminate a figure that moves relative to a ground texture. This computation of relative movement relies on a more complex algorithm, one which detects discontinuities in the movement field. The experiments described in this paper indicate that the outputs of neighbouring movement detectors interact in a multiplication-like fashion and then in turn inhibit locally the flicker detectors. The following main characteristic properties (partly a direct consequence of the algorithm's structure) have been established experimentally: a) Coherent motion of figure and ground inhibit the position detectors whereas incoherent motion fails to produce inhibition near the edges of the moving figure (provided the textures of figure and ground are similar). b) The movement detectors underlying this particular computation are direction-insensitive at input frequencies (at the photoreceptor level) above 2.3 Hz. They become increasingly direction-sensitive for lower input frequencies. c) At higher input frequencies the fly cannot discriminate an object against a texture oscillating at the same frequency and amplitude at 0° and 180° phase, whereas 90° or 270° phase shift between figure and ground oscillations yields maximum discrimination. d) Under conditions of coherent movement, strong spatial incoherence is detected by the same mechanism. The algorithm underlying the relative movement computation is further discussed as an example of a coherence measuring process, operating on the outputs of an array of movement detectors. Possible neural correlates are also mentioned.     

DLS 5.0 - The Biomechanical Effects of Dynamic Locking Screws

Introduction

Indirect reduction of dia-/metaphyseal fractures with minimally invasive implant application bridges the fracture zone in order to protect the soft-tissue and blood supply. The goal of this fixation strategy is to allow stable motion at the fracture site to achieve indirect bone healing with callus formation. However, concerns have arisen that the high axial stiffness and eccentric position of locked plating constructs may suppress interfragmentary motion and callus formation, particularly under the plate. The reason for this is an asymmetric fracture movement. The biological need for sufficient callus formation and secondary bone healing is three-dimensional micro movement in the fracture zone. The DLS was designed to allow for increased fracture site motion. The purpose of the current study was to determine the biomechanical effect of the DLS_5.0.

Methods

Twelve surrogate bone models were used for analyzing the characteristics of the DLS_5.0. The axial stiffness and the interfragmentary motion of locked plating constructs with DLS were compared to conventional constructs with Locking Head Screws (LS_5.0). A quasi-static axial load of 0 to 2.5 kN was applied. Relative motion was measured.

Results

The dynamic system showed a biphasic axial stiffness distribution and provided a significant reduction of the initial axial stiffness of 74.4%. Additionally, the interfragmentary motion at the near cortex increased significantly from 0.033 mm to 0.210 mm (at 200N).

Conclusions

The DLS may ultimately be an improvement over the angular stable plate osteosynthesis. The advantages of the angular stability are not only preserved but even supplemented by a dynamic element which leads to homogenous fracture movement and to a potentially uniform callus distribution.     

Muscle energy transfer during a given wave-like movement of human body segments

The paper deals with a movement of two voluntary segments fixed in a joint and connected by a muscle in a multi-segment biomechanical system of human body. The muscle model is a four-element mechanical system. The mechanical movement energy brought into the "segments-muscle" system from the segments preceding the next ones is studied. The movement in which the total multi-segment system of the human body participates is described by the wave equation. Conditions concerning applying active muscle efforts and correlating velocities of muscle ends movement which provide the maximal value of transferred energy have been found. It is shown that the use of "artificial muscles" type devices promotes activization of energy transfer processes between segments.     

A simple method for recording body temperature in insects

Application of thermocouples for measuring body temperature of insects is described in experiments on American cockroach (Periplaneta americana). The temperature of the head, mesothorax and abdomen was measured at rest and during flight. The overall accuracy of the measuring system was +/- 0.1 degrees C.     

Design and testing of a novel measuring system for use in dental biomechanics--principles and examples of measurements with the hexapod measuring system]

A novel measuring set-up based on a hexapod system for use in dental biomechanics is described. It was specially developed to measure force/deflection characteristics of different dental materials and devices. The functionability and suitability of the system for use in experimental biomechanics were investigated in two different studies. In a first study the micro mobility of prosthetic telescopic crowns prior to and after simulated wear was determined to investigate the influence of wear processes on the stability of the anchorage elements and thus of prostheses. This study investigated the ability of the setup to load a specimen with high forces or torques of up to 100 Newton. The second study looked at the force/deflection characteristics of orthodontic anchorage pins used in orthodontics to additionally stabilize the anchorage unit, for example during molar movement. In this study specimens were loaded with small forces of less than 10 Newton, as are typically used in orthodontics. Using the setup, the deflection behaviour of these devices under high and low loading was measured at a resolution of approximately one micrometer or one angular second.     

Non-contact measuring of small translations and rotations in all degrees of displacement]

The investigation of biomechanical problems often makes it necessary to measure displacements and rotations in space. An easy-to-handle optical measuring system has been developed that permits non-contact simultaneous determination of small translations and rotations in all degrees of freedom. Three two-dimensional light-sensitive sensors (PSD [position sensing detector] elements) were arranged spatially to form a measuring sensor. After processing in a computer, the signals definitively determine relative shift and rotation. Thus it is possible, for example, to measure the relative movement between two adjacent spinal vertebrae under different loads.     

Microfracture patterns of abrasive wear striations on teeth indicate directionality

A method is described that will indicate the direction that an abrasive particle was traveling as it scored the surface of a brittle material. Light and scanning electron micrographs of glass, dentine, and enamel abraded by loose sand, steel carbide, and diamond indicate that partial Hertzian fracture cones are formed at the margins of wear striations during abrasion. The bases of these fracture cones face in the direction of travel of the abrasive particle and, therefore, indicate directionality. Because this method is based only on the consistent geometry of fracturing of brittle materials, it is independent of the loading of the abrasive particle. The only other method available to determine directionality of striations is unreliable since it uses the width of striations, and, hence, is dependent upon a consistent loading regime of the abrasive particle. This new method has direct application for determining the direction of movement of the jaws during mastication in living or fossil animals.     

Using Eye Movements to Evaluate the Cognitive Processes Involved in Text Comprehension

The present article describes how to use eye tracking methodologies to study the cognitive processes involved in text comprehension. Measuring eye movements during reading is one of the most precise methods for measuring moment-by-moment (online) processing demands during text comprehension. Cognitive processing demands are reflected by several aspects of eye movement behavior, such as fixation duration, number of fixations, and number of regressions (returning to prior parts of a text). Important properties of eye tracking equipment that researchers need to consider are described, including how frequently the eye position is measured (sampling rate), accuracy of determining eye position, how much head movement is allowed, and ease of use. Also described are properties of stimuli that influence eye movements that need to be controlled in studies of text comprehension, such as the position, frequency, and length of target words. Procedural recommendations related to preparing the participant, setting up and calibrating the equipment, and running a study are given. Representative results are presented to illustrate how data can be evaluated. Although the methodology is described in terms of reading comprehension, much of the information presented can be applied to any study in which participants read verbal stimuli.     

Verfahren und Analysenautomat zur Bestimmung von Nährlösungskomponenten und Stoffwechselprodukten

A continuous flow system with an enzyme electrode and with a new type of measuring instrument, the BIOXY-Meter, is described as an example for the determination of glucose. The BIOXY-Meter combined with various biosensors may be used in biotechnology and in other fields for the solution of a number of analytical problems. Measuring principle is the reduction of oxygen. The peak of first derivation of the current-time-curve is proportional to oxygen consumption and to decrease of substrate concentration. Enzyme fixation with common adhesive and a device for automated saturation of measuring samples with air in the sampler are also described. With the apparatus 60 samples per hour are analyzed for glucose. The linear measuring range is 0.1 mMol to 1.5 mMol with a coefficient of variation of V_k = 0.93 per cent. The described type of enzyme electrode is stable for 2 to 12 weeks or 1,000 to 5,000 measurements.     

Biomechanical Comparison of Different Stabilization Constructs for Unstable Posterior Wall Fractures of Acetabulum. A Cadaveric Study

Purpose

Operative treatment of unstable posterior wall fractures of acetabulum has been widely recommended. This laboratory study was undertaken to evaluate static fixation strength of three common fixation constructs: interfragmentary screws alone, in combination with conventional reconstruction plate, or locking reconstruction plate.

Methods

Six formalin-preserved cadaveric pelvises were used for this investigation. A posterior wall fracture was created along an arc of 40–90 degree about the acetabular rim. Three groups of different fixation constructs (two interfragmentary screws alone; two interfragmentary screws and a conventional reconstruction plate; two interfragmentary screws and a locking reconstruction) were compared. Pelvises were axial loaded with six cycles of 1500 N. Dislocation of superior and inferior fracture site was analysed with a multidirectional ultrasonic measuring system. Results: No statistically significant difference was found at each of the superior and inferior fracture sites between the three types of fixation. In each group, the vector dislocation at superior fracture site was significantly larger than inferior one.

Conclusions

All those three described fixation constructs can provide sufficient stability for posterior acetabular fractures and allow early mobilization under experimental conditions. Higher posterior acetabular fracture line, transecting the weight-bearing surface, may indicate a substantial increase in instability, and need more stable pattern of fixation.     

Design and performance of a fracture monitoring transducer

The answer to the question, ‘when is a fracture healed?’ is not simple, since the healing process is progressive and it is not possible to specify a time when the fracture can be said to have healed. In the past the assessment of fracture healing has, in the main, been subjective, relying upon the skill of the interpreter. A more objective method would be an advantage for many reasons, and since the bone is intended to be load bearing it is reasonable to assess healing by measuring the mechanical integrity of the bone. to do this a ‘clamp on’ transducer has been developed which, when fitted to the support column of an external fixator, enables the stiffness of a fracture to be determined during the healing process. Over the past 6 years this system has been used for both clinical and research work. It has enabled various forms of treatment to be evaluated in terms of ‘rate of healing’ and it also indicates the safe point at which the fixator can be removed.